An engine of a vehicle may be automatically stopped during vehicle operation to conserve fuel. The engine may also be automatically restarted in response to operating conditions. If a driver depresses an accelerator pedal or applies another device to command a vehicle to move, it may be desirable to restart engine quickly so that the vehicle and engine may comply with the driver's request. If the vehicle and engine do not comply with the driver's request in a timely manner, the driver may be dissatisfied with the vehicle's response. One way to improve engine and vehicle response to the driver's request is to inject fuel to engine cylinders when an intake valve of the cylinder receiving fuel is open so that the engine may be started in a shorter time period. However, open valve fuel injection may allow fuel to impinge on cylinder walls and enter the engine crankcase or reduce the oil film on cylinder walls.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: ceasing combustion in engine cylinders; port injecting fuel to a first cylinder while the engine is rotating and intake valves of the first cylinder are closed; stopping the engine without inducting the port injected fuel into the first cylinder; and combusting the port injected fuel in the first cylinder after port injecting fuel to a second cylinder while intake valves of the second cylinder are open.
By port injecting fuel to cylinders having closed intake valves during engine stopping, it may be possible to improve fuel vaporization for engine cylinders that are not provided fuel during open valve conditions for a first engine cycle since engine stop. For example, fuel may be injected before engine stop to a first group of engine cylinders that have closed intake valves near the end of engine shutdown (e.g., a time from an engine stop request to actual engine stop) and during engine stop. Injecting fuel to a closed intake valve may improve the possibility of vaporizing the port injected fuel as an amount of time the fuel is in contact with a warm engine intake valve or cylinder intake port increases. After a request to restart the engine, fuel may be port injected to a second group of cylinders that have open intake valves to reduce engine starting time. Fuel that was injected to a closed intake valve as the engine neared a stopped state may be drawn into cylinders in a vaporized state as the engine rotates and the intake valves open.
Thus, a portion of engine cylinders may receive open valve injected fuel during a first cylinder cycle since engine stop while another portion of engine cylinders induct fuel that was injected to a closed intake valve during engine stopping. In this way, the engine may be quickly started via open valve injection, and engine emissions and combustion stability may be improved via closed valve injection. Further, since less than all engine cylinders receive open valve injection during engine restarting, the amount of fuel that encounters cylinder walls and enters the engine crankcase may be reduced.
The present description may provide several advantages. Specifically, the approach may improve engine emissions and combustion stability during engine starting. Further, the approach may improve engine starting when fuels having higher concentrations of alcohol are injected to the engine. Further still, the approach may reduce the possibility of engine degradation by reducing the amount of liquid fuel that enters engine cylinders.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.